如何重构具有不同签名但几乎相同的主体的方法？

Question

Given this private method:

private static IEnumerable<LedgerSummary> FilterLedgers(IList<LedgerSummary> ledgers, List<ExcludedLedgerAccount> excludedLedgerAccounts)
{
    var excludedLedgerEntries = ledgers.Where(x => excludedLedgerAccounts.Any(y => y.LedgerAccount == x.LedgerAccount)).ToList();

    var filteredLedgers = ledgers.Except(excludedLedgerEntries).ToList();

    // do some more filtering

    return filteredLedgers;
}

and this one:

private static IEnumerable<LedgerPosting> FilterLedgers(IList<LedgerPosting> ledgers, List<ExcludedLedgerAccount> excludedLedgerAccounts)
{
    var excludedLedgerEntries = ledgers.Where(x => excludedLedgerAccounts.Any(y => y.LedgerAccount == x.DistributionAccountLedgerAccount)).ToList();

    var filteredLedgers = ledgers.Except(excludedLedgerEntries).ToList();

    // do some more filtering

    return filteredLedgers;
}

what's the best way to refactor them so that I'm not repeating what is essentially the same logic in the method bodies?

The reason why it's not so straightforward ( in my mind ) is because the method signatures are slightly different in that one's taking (and returning) a ' List ' of LedgerSummary s and the other LedgerPostings s, and each of these have different property names (that map to the same properties in ExcludedLedgerAccount ).

Unfortunately, I can't change the properties in either of those two classes or to use a common interface, for example, for reasons that would lengthen this discourse!

I know the answer's really straightforward (so I apologise in advance) but I seem to be having a programmer's block at the minute.

Answer 1

Try something like this (don't have a VS at hand now, might require a bit of debugging)

private static IEnumerable<T> FilterLedgers<T> FilterLedgers(
    IList<T> ledgers, 
    List<ExcludedLedgerAccount> excludedLedgerAccounts,
    Func<T, ExcludedLedgerAccount, bool> selector)
{
    var excludedLedgerEntries = ledgers.Where(x => excludedLedgerAccounts.Any(y => selector(x, y)).ToList();

    var filteredLedgers = ledgers.Except(excludedLedgerEntries).ToList();

    // do some more filtering

    return filteredLedgers;
}

And use it:

IEnumerable<LedgerSummary> result = FilterLedgers<LedgerSummary>(input, exclude, (i, e) => i.LedgerAccount == e.LedgerAccount);

IEnumerable<LedgerPosting> result = FilterLedgers<LedgerSummary>(input, exclude, (i, e) => i.LedgerAccount == e.DistributionAccountLedgerAccount);

Answer 2

You can extract a predicate that you're using in the Any extension method:

private static IEnumerable<LedgerSummary> FilterLedgersImpl(IEnumerable<LedgerSummary> ledgers, Func<LedgerSummary, LedgerAccount, bool> predicate)
{
    var excludedLedgerEntries = 
        ledgers
           .Where(x => excludedLedgerAccounts.Any(y => predicate(x, y)))
           .ToList();

    var filteredLedgers = ledgers.Except(excludedLedgerEntries).ToList();

    // do some more filtering

    return filteredLedgers;
}

And then you can use this helper method directly:

var list1 = FilderLedgersImpl(ledgers, (x, y) => y.LedgerAccount == x.LedgerAccount);

var list2 = FilderLedgersImpl(ledgers, (x, y) => y.LedgerAccount == x.DistributionAccountLedgerAccount);

Answer 3

Unless LedgerSummary and LedgerPosting share a common base class that does all the work you need (in which case you could use generics), you can't do much with this.

In C++, you could use templates (or even typedefs) for a nice solution but not in C# or java... unless you wanted to use a code generator.